G. Cloutier et Kk. Shung, CYCLIC VARIATION OF THE POWER OF ULTRASONIC DOPPLER SIGNALS BACKSCATTERED BY POLYSTYRENE MICROSPHERES AND PORCINE ERYTHROCYTE SUSPENSIONS, IEEE transactions on biomedical engineering, 40(9), 1993, pp. 953-962
Factors affecting the power of the ultrasonic Doppler signal within th
e flow cycle have been evaluated experimentally using a pulsatile flow
loop model. Polystyrene microspheres and porcine red cells suspended
in saline solution for hematocrits between 2 and 40% were used as scat
tering fluid in the flow model. Experiments were performed at mean flo
w velocities of 11, 64, and 76 cm/s. In laminar flow experiments perfo
rmed at a mean velocity of 11 cm/s, no variation of the Doppler power
was found for both polystyrene microspheres and red cell suspensions (
40% hematocrit). When turbulence was induced in the flow model, the po
wer increased during systole, a maximum was observed early after peak
systole, and a decrease was obtained in diastole during deceleration o
f flow. At higher mean flow velocities (64 and 76 cm/s), a significant
cyclic variation of the Doppler power was also measured for all value
s of hematocrits (between 2 and 40%). The power of the signal scattere
d by microspheres and red cell suspensions at 4% hematocrit dropped in
systole, reached a minimum at peak systole, and then increased during
early diastole. For red cells suspended in saline at 40% hematocrit,
a slightly different pattern of variation was obtained. The cyclic var
iations observed at high flow velocities and in the presence of turbul
ence are believed to be associated with cyclic changes in the correlat
ion among particles. In the present study, the effect of red cell aggr
egation on the cyclic variation has not been addressed.